HATCHING THE EGGS. 137 



shallovtTbox with a glass bottom. Pour in a little water, 

 and put the eggs to be examined in the water ; then 

 by looking from above or below, but especially from 

 below, you can see very distinctly what is inside the 

 egg. This method obviates the distortion sometimes 

 produced by refraction in the homoeopathic phial. 



You will soon be very anxious to ascertain how 

 large a percentage of the eggs is impregnated. 



It has been usually thought that the impregnated 

 eggs could not be told from the empty ones previous 

 to the formation of the embryotic line, which is the 

 spine of the fish, and which appears when about one 

 third of the period of incubation * is accomplished. 

 This, however, is not strictly true, because there is 

 a period, within forty-eight hours of the taking of the 

 eggs, when the good eggs can be distinguished from 

 the worthless ones. The distinction is this, that in 

 the unimpregnated eggs a small annular disk, with 

 a much smaller round dot in the centre, will be seen 

 at the top of the egg, and will remain there until 

 the eggs turn white, while in the impregnated egg 

 the disk will disappear within twenty-four hours. 

 The eggs, then, which after the first day present the 

 disk, are unimpregnated. Those in which the disk is 

 not visible are impregnated. The explanation of this 

 is as follows. 



* The word " incubation " from in and cubo> " to sit on," 

 has been used in reference to the hatching of bird's eggs by 

 steam, and seems to be equally allowable in this application for 

 the hatching of fish eggs. There is no sitting upon the eggs in 

 either case. 



